Osaka enjoyed a remarkable rise up the world rankings after first linking up with Bajin in the 2017 off-season.
The Japanese player climbed from world No.72 to reach the top five during the course of 2018, when she won her first grand slam title, and then hit top spot after her success in Melbourne.
Bajin, who has previously worked as a hitting partner for Serena Williams, Caroline Wozniacki, Sloane Stephens and Victoria Azarenka, was named WTA coach of the year in 2018.
«Thank you Naomi I wish you nothing but the best as well. What a ride that was. Thank you for letting me be part of this,» he responded to Osaka’s tweet.